Copysheets and their preparation



United States Patent C) 3,153,591 COPYSHEETS AND THEIR PREPARATION Byron W. Neher, Hudson, Wis., assignor to Minnesota Mining and Manufacturing Company, St. Paul, Minn., a corporation of Delaware No Drawing. Filed June 25, 1962, Ser. No. 205,086 8 Claims. (Cl. 96-1) This invention relates to sensitized photoconductive copysheets and a process for the preparation thereof. In one aspect, this invention relates to photoconductive zinc oxide copysheets having improved spectral sensitivity.

A recently developed image reproduction process involves electrolytically developing permanent and visible images on suitable, strongly photoconducitve copysheets after exposure to light images. This method, described more fully in United States Patent Number 3,010,883, includes the electrolysis of an electrolytic developer and particularly the selective electrodeposition of a metallic or other visibly contrasting indicia at the exposed portions of the photoconductive surface, eg, by electrolytic reduction. Strongly photoconductive copysheets suitable for the above method are described in United States Patent Number 3,010,884. To improve the sensitivity of photoconductive copysheets for use in electrolytic and electrostatic processes, various dye sensitizers, such as acridine orange, have been suggested. However, since sensitizers employed in silver halide emulsions are not necessarily useful in photoconductive copysheets, new sensitizing compounds have been desired. Although the ability to make selective exposures through colored filters permits the reproduction of natural colors on such photoconductive copysheets, color reproduction generally requires a photoconductive copysheet having panchromatic response.

One object of this invention is to provide a process for the preparation of photoconductive copysheets having improved spectral response.

A further object of this invention is to provide a strongly photoconductive copysheet having improved sensitivity without objectional sheet color.

Still another object of this invention is to provide a strongly photoconductive copysheet having improved sensitivity in the blue region of the light spectrum.

In accordance with this invention, photoconductive copysheets having increased spectral sensitivity are obtained by incorporating a 4-amino-naphthalimide in. the photoconductive layer of the copysheet. The amount of the 4-amiuo-naphthalimide may vary widely, depending on the sensitivity desired. For many applications in which a white copysheet is desired, the sensitizer concentration preferably is not used in such quantity as would significantly affect the color or appearance of the sheet. Generally, from about 0.005 to about 2,000 parts by Weight of the 4-arnino-naphthalimide per 40,000 parts by weight of photoconductive material in the photoconductive layer may be employed. 4-amino-naphthalimides have been used commercially for textile and other dyeing purposes. However, sensitizing dyes are generally considered to be dyes of low light fastness and are believed to function by absorbing light energy and transferring such absorbed energy to the sensitized material, the dyes themselves being degraded in this process. Consequently, photographic sensitizers, i.e. sensitizers used in silver halide emulsions, seldom are found in commercial dyeing applications, Where light fastness is a requisite. It is therefore quite surprising that the 4-amino-naphthalimides serve as sensitizers for photoconductive compounds, such as zinc oxide, indium oxide, etc.

Preferred 4-arnino-naphthalimide dyes which can be used in this invention include those of the formula wherein Z and Z are hydrogen or SO M and M is hydrogen or a cation such as sodium, etc. R and R are hydrogen, alkyl (e.g. methyl, propyl, hexyl, etc.); aryl (e.g. phenyl, tolyl), and alkaryl (e.g. benzyl, etc.). Y is hydrogen, amino (including substituted amino, such as phenylamino, etc.), alkyl (e.g. methyl, ethyl, propyl, hexyl, carhoxymethyl, sulfoethyl, 3-arnido propyl, etc.), alkaryl (e.g. benzyl, etc.), aryl (e.g. tolyl, carboxy phenyl, sulfophenyl, hydroxyphenyl, dialkylaminophenyl, naphthyl, 4-carboxy-3-hydroxy-phenyl, etc.) and heterocyclic (e.g. 2-pyridyl, Z-thiazolyl, etc.). At least one of R and R is preferably hydrogen. As used herein, alkyl, aryl and aralkyl include both the substituted and unsubstituted radicals. Suitable 4-arnino-naphthalimides and their preparation are described in US. 2,096,295 and 2,455,095 and in references cited therein, such being incorporated herein by reference. The yellow colored 4- amino-naphthalimide dyes provide enhanced blue sensitivity in photoconductive layers.

As stated above, the preparation of the 4-amino-naph thalimides of this invention is described in the chemical literature. For example, acenaphthene may be nitrated, then oxidized and the nitro group reduced by the procedures set forth on pages 81-85 of the report entitled I. G. Farbenindustrie Manufacture of Triphenylmethane Dyestuffs and Intermediates at Ludwigshafen and Hoechst (British Intelligence Objectives Sub-Committee, 32, Bryanston Square, London W.1., October-December 1955).

The following illustrates one technique for using a 4-aniino-naphthalimide to sensitize a photoconductive powder:

630 grams of photoconductor grade zinc oxide together with 314 grams of a butadiene-styrene (30:70 mol ratio) copolymer and 615 grams of toluene are ball milled together for 10 hours. To one-hundred grams of the resulting dispersion is then added 1.5 milliliters of a 0.5% solution of the 4-amino-naphthalirnide dye in methanol, dirnethylformamide or suitable solvent not adversely affecting the properties of the ultimate coated sheet. Since commercial dyes are usually impure and of varying composition, more consistent and uniform results are usually obtained if the dye is first crystallized from aqueous ethanol. The sensitized dispersion is then coated by a suitable means, such as a knife coater, onto an electrically conductive support, such as an aluminum sheet or an aluminum-paper laminate. After the coating dries and the coated paper is dark adapted, the light sensitive sheet may be exposed to blue or white light and electrolytically developed, as described in U.S.

Patented Oct. 20, 1964:

3,010,883. If a wedge spectrum is used for the exposure, the sensitization maximum can be found. The range of sensitization generally extends from below 4000 A. to 47004800 A., the exact region of sensitization being N dependent on the particular 4-amin0-naphthalimide em- 5 ployed. For example, the following 4-amino-naphtha- I limides may be used to provide a marked increase in blue sensitivity when tested in the aforementioned manner. 1%

O: \C=O {T112 I N- (2py1'idy1) A-amino-naphthalimide -aminonaphthalimide 4-amino-3,x-disulf0naphtha1imide (M H or -N C2H5) a CIHQCH2SO H I -S /N OQNa I I E20 NH;

. N- (p-tolyl) -4-amin0-3-su1f0naph thalimide (Brilliant Sulfoflavine I FA', CI. 56205) I NNZ 00 11 N- fi-sulfoethyl) -4-aminonaphtl1a1imide H O H -CC H3 I r N N o=o b=o 0:0

I 1 113 NH; 2 N-is0pr0py1-4amino-flaphthalimide 6O N-(-hydroxy-S-carb0xypheny1)-4-amino-3-sulfonaphthulimidc I I N NHE N fl N- p-tolyl) -4-aminonaphtha1imide N- (ptolyl) Aamino-3,x-disulfonaphthalimide (3143129 N the S 0 11 I'm 2 N-tetradecyl--amino-3,x-disulfonaphthalimide l H CH N- (p-tolyl) -4-methylarnino-3-su1ph0naphthalimide 11 0 CH; N- (p-tolyl) 4-di1nethy1amino 3-sulphonaphthalimide NH; N-amino-4-amino-3-sulph0naphthalimide CtHflT rately with mixing between additions, both being in 0.1%

solution in a 50/50 weight ratio mixture of methanol and methyl ethyl ketone. The resulting coated sheet displayed good panchromatic response. The inclusion of Setoflavine (CI. 49005) may also enhance the response of the photoconductive coating.

Depending on the solubility characteristics of the 4- amino-naphthalimide, various inert solvents'may be used to dissolve the sensitizer, including dimethyl formamide, toluene, methyl-isobutyl ketone, ethanol, etc. Triethylamine or other bases often are of value for preparing those salts of carboxy or sulfo containing dyes which are more soluble in certain organic solvent systems. However, in many instances, mere ball milling the solid sensitizer into the dispersion will produce adequate sensitization.

Although the quantity of sensitizing dye can be varied widely, the sensitivity of photoconductive zinc oxide coat ings has been found to increase with increasing dye concentration. As mentioned earlier, the upper limit of dye concentration is generally limited by the amount of copysheet discoloration that can be tolerated. The optimum amount of sensitizer used is selected to provide the desired sensitization without objectionable sheet discoloration.

Various other embodiments of the present invention will be apparent to those skilled in the art without departing from the scope thereof.

I claim:

1. A sensitized photoconductive copysheet having a light sensitive layer comprising a photoconductive powder selected from the group consisting of zinc oxide and indium oxide and, in intimate association therewith, between about 0.005 and about 2,000 parts by weight of a 4 amino-naphthalimide per 40,000 parts of said strongly photoconductive powder to increase the light sensitivity thereof.

2. A sensitized photoconductive copysheet having a light sensitive layer comprising a photoconductive zinc oxide powder and, in intimate association therewith, between about 0.005 and about 2,000 parts by weight of a 4-amino-naphthalimide per 40,000 parts of said zinc oxide to increase the light sensitivity thereof.

3. A sensitized photoconductive copysheet having a light sensitive layer comprising a photoconductive zinc oxide powder and an insulating binder, said light sensitive layer having a sufiicient quantity of a 4-amino-naphthalimide to increase the light sensitivity thereof.

4. A photoconductive composition comprising a photoconductive powder selected from the group consisting of zinc oxide and indium oxide, an insulating binder therefor, and a 4-arnino-naphthalimide to increase the light sensitivity of said photoconductive powder.

5. A photoconductive composition comprising photoconductive zinc oxide powder, an insulaintg' binder therefor, and a 4-amino-naphthalimide to increase the light sensitivity of said zinc oxide powder.

6. A light sensitized photoconductive construction having a light sensitive layer comprising a strongly photoconductive powder selected from the group consisting of zinc oxide and indium oxide and, in intimate association therewith, a suiiicient quantity of a 4-amino-naphthalamide to increase the light sensitivity thereof.

7. A sensitized photoconductive copysheet having a light sensitive layer comprising a photoconductive powder selected from the group consisting of zinc oxide and indium oxide and, in intimate association therewith, between about 0.005 and about 2,000 parts by weight of a 4- amino-naphthalamide per 40,000 parts of said photoconductive powder to increase the light sensitivity thereof.

8. A sensitized photoconductive copysheet having a light sensitive layer comprising a photoconductive zinc oxide powder and, in intimate association therewith, between about 0.005 and about 2,000 parts by Weight of a 4-amino-naphthalamide per 40,000 parts of said zinc oxide to increase the light sensitivity thereof, the quantity of said 4-aminornaphthalamide being insufficient to sig nificantly afiect the color of said layer.

References Cited in the file of this patent OTHER REFERENCES Bube: Photoconductivity of Solids (1960), Preface xii-xiii. 

1. A SENSITIZED PHOTOCONDUCTIVE COPYSHEET HAVING A LIGHT SENSITIVE LAYER COMPRISING A PHOTOCONDUCTIVE POWDER SELECTED FROM THE GROUP CONSISTING OF ZINC OXIDE AND INDIUM OXIDE AND, IN INTIMATE ASSOCIATION THEREWITH, BETWEEN ABOUT 0.0005 AND BAOUT 2,000 PARTS BY WEIGHT OF A 4AMINO-NAPHTHALIMIDE PER 40,000 PARTS OF SAID STRONGLY PHOTOCONDUCTIVE POWDER TO INCREASE THE LIGHT SENSITIVITY THEREOF. 